In the same way, the regex expression (?-i)[e-f] should match, for instance, the lower-case letters e and f and all Latin accentuated forms of the letter e. In other words, it should be equivalent to the regex (?-i)[eèéêëēĕėęěẹẻẽếềểễệ℮f], if I consider, simply, the Courier New font !